Which Of These Animals Has The Same Type Of Symmetry As A Vertebrate?

27.2A: Animal Characterization Based on Body Symmetry

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Folio ID

13693

Animals can be classified past three types of body plan symmetry: radial symmetry, bilateral symmetry, and disproportion.

Learning Objectives

• Differentiate amongst the means in which animals tin be characterized by body symmetry

Key Points

• Animals with radial symmetry accept no right or left sides, only a height or bottom; these species are usually marine organisms similar jellyfish and corals.
• Most animals are bilaterally symmetrical with a line of symmetry dividing their torso into left and right sides forth with a "caput" and "tail" in addition to a tiptop and lesser.
• Only sponges (phylum Porifera) take asymmetrical body plans.
• Some animals outset life with 1 type of body symmetry, merely develop a dissimilar type as adults; for case, sea stars are classified as bilaterally symmetrical fifty-fifty though their adult forms are radially symmetrical.

Fundamental Terms

• sagittal plane: divides the body into right and left halves
• radial symmetry: a course of symmetry wherein identical parts are bundled in a circular fashion around a key axis
• bilateral symmetry: having equal system of parts (symmetry) near a vertical plane running from head to tail

Animal Label Based on Body Symmetry

At a very basic level of classification, true animals tin be largely divided into three groups based on the blazon of symmetry of their body plan: radially symmetrical, bilaterally symmetrical, and asymmetrical. Only a few fauna groups brandish radial symmetry, while asymmetry is a unique feature of phyla Porifera (sponges). All types of symmetry are well suited to see the unique demands of a particular animal's lifestyle.

Radial Symmetry

Radial symmetry is the arrangement of torso parts around a central centrality, like rays on a sun or pieces in a pie. Radially symmetrical animals have elevation and bottom surfaces, but no left and right sides, or forepart and back. The ii halves of a radially symmetrical animal may exist described as the side with a mouth ("oral side") and the side without a oral fissure ("aboral side"). This form of symmetry marks the torso plans of animals in the phyla Ctenophora (comb jellies) and Cnidaria (corals, sea anemones, and other jellies). Radial symmetry enables these sea creatures, which may be sedentary or simply capable of slow movement or floating, to experience the environment equally from all directions.

Figure \(\PageIndex{1}\): Radial symmetry: Some organisms, like sea anemones (phylum Cnidaria), have radial symmetry.

Bilateral Symmetry

Bilateral symmetry involves the division of the animal through a sagittal aeroplane, resulting in ii mirror-epitome, right and left halves, such equally those of a butterfly, crab, or human body. Animals with bilateral symmetry have a "head" and "tail" (anterior vs. posterior), front and back (dorsal vs. ventral), and right and left sides. All true animals, except those with radial symmetry, are bilaterally symmetrical. The development of bilateral symmetry and, therefore, the formation of anterior and posterior (head and tail) ends promoted a phenomenon called cephalization, which refers to the collection of an organized nervous system at the animal'southward anterior end. In contrast to radial symmetry, which is all-time suited for stationary or limited-movement lifestyles, bilateral symmetry allows for streamlined and directional motion. In evolutionary terms, this elementary form of symmetry promoted active mobility and increased composure of resource-seeking and predator-casualty relationships.

Figure \(\PageIndex{1}\): Bilateral symmetry: This monarch butterfly demonstrates bilateral symmetry down the sagittal plane, with the line of symmetry running from ventral to dorsal and dividing the body into two left and right halves.

Animals in the phylum Echinodermata (such as body of water stars, sand dollars, and body of water urchins) display radial symmetry as adults, but their larval stages exhibit bilateral symmetry. This is termed secondary radial symmetry. They are believed to have evolved from bilaterally symmetrical animals; thus, they are classified as bilaterally symmetrical.

Figure \(\PageIndex{i}\): Secondary radial symmetry in echinoderms: The larvae of echinoderms (sea stars, sand dollars, and sea urchins) have bilateral symmetry as larvae, but develop radial symmetry as full adults.

Asymmetry

Only members of the phylum Porifera (sponges) accept no trunk programme symmetry. In that location are some fish species, such equally flounder, that lack symmetry every bit adults. All the same, the larval fish are bilaterally symmetrical.

Source: https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book:_General_Biology_%28Boundless%29/27:_Introduction_to_Animal_Diversity/27.2:_Features_Used_to_Classify_Animals/27.2A:_Animal_Characterization_Based_on_Body_Symmetry

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